The present invention resides in the field of assays to determine the capacity of blood platelets to aggregate.
By way of background, the ability of animals to selectively form blood clots in areas of trauma is a vital function. Failure of the blood to clot, of course, can lead to severe hemorrhage and in some instances eventual fatality. On the other hand, uncontrolled clotting or coagulation of the blood within vessels can also lead to serious complications. In light of these and other complications related to blood clotting, there has naturally been a great desire to develop tests which can be used to measure clotting tendencies and to determine the cause of any abnormalities, as well as methods and materials for treating bleeding sites.
A number of tests have been developed to monitor or determine the causes of abnormal blood clotting tendencies. Although these known tests have in some instances proven acceptable to some extent, especially in light of the desire to improve the human condition, there is a continuing need for even more sensitive blood clotting tests which give consistent and reproducible results. Additionally, improvements need to be made in the reagents for these prior art tests, which are commonly turbid or include undesirable particulate matter, and which have solid, non-soluble activating species, which fact is borne out by filtering these prior art reagents and noting substantial if not complete loss of coagulation activating ability. Further, there is an ever-present need for new assays for accurately monitoring or determining clotting conditions for which there are no known accurate tests.
For example, one general coagulation test procedure which has been developed is the activated partial thromboplastin time (also commonly referred to as the aPTT). Early on, a typical aPTT test was conducted by incubating a citrated plasma sample in contact with a solid material, such as glass, celite or kaolin, known to activate Factor XII (Hagemann Factor). Then, Ca.sup.2+ ion and a platelet substitute (i.e. a phospholipid such as a cephalin derived from brain tissue or soy bean) was added to the sample, and the time necessary for the sample to clot was measured. More recently, commercial aPTT reagents have been developed which include the platelet substitute and a chemical known to activate Hagemann Factor, such as ellagic acid. For example, commercial aPTT reagents are available from Dade Division of Baxter Travenol, of Miami, Fla., Ortho Diagnostics of Raritan, N.J., and Nyegaard A.S. of Norway. In a typical use, these commercial aPTT reagents are added to a citrated plasma sample which is then incubated for a period of time (commonly about 5 minutes) for activation to occur. Ca.sup.2+ is then added to the sample, often in the form of CaCl.sub.2, and the time necessary for clotting is measured. However, these aPTT reagents have proven to be unsatisfactory in many aspects because they are not sensitive enough to heparin, Factor deficiencies, or other causes of abnormal clotting tendencies. Also, these commercial reagents give sporadic and unreproducible results in some instances, problems which some have attributed to the presence of particulate or otherwise non-dissolved matter in the reagents. Also, the activator in these commercial reagents is not in solution, a fact which is confirmed by filtering the reagents and noting a substantial or complete loss of activating behavior.
Another generally known coagulation test procedure is the Activated Whole Blood Coagulation Time (AWBCT). Typical known AWBCT tests are performed by placing a whole blood specimen in a test tube containing solid particulate material such as celite for activation of Hagemann Factor. Thereafter, the sample is heated and agitated, and the time necessary for the sample to clot is measured. As with the known aPTT tests, however, these prior art AWBCT tests often give unreliable and unreproducible results. This could result from activation with the solid particulate material. Activation in this manner tends to be non-uniform and to interfere with normal coagulation mechanisms due to adsorption of Factors and other materials to the solid particles.
In addition to the above-noted shortcomings of known tests and reagents, there has been a more wholesale failure in this area in providing blood clotting tests which are sensitive to the activity of blood platelets in the coagulation scheme. This is despite the existence of very numerous disorders and treatments which impact platelet activity.
For example, one condition which is known to affect platelet activity is systemic lupus. This form of lupus is thought to be attributable to the presence of "lupus anticoagulant", which is an antiphospholipid antibody which inhibits the action of Platelet Factor 3 (PF3) in the coagulation mechanism. One test which has been suggested for use in detecting lupus anticoagulant is an ACT test performed on platelet poor plasma using kaolin to activate Hagemann Factor. T. Exner et al., British Journal of Haematology, 1978, 40, 143-151. While Exner et al. reported successfully detecting lupus anticoagulant using their method, it nonetheless involves using solid particulate material for activation which, as discussed above, can lead to decreased sensitivity and consistency from test to test.
The Tissue Thromboplastin Inhibition Procedure (TTI), M. Boxer et al., Arthritis Rheum., 19:1244 (1976); M. A. Schleider et al., Blood, 1976, 48, 499-509, and the Platelet Neutralization Procedure (PNP), D. A. Triplett et al., A.J.C.P., 79 No. 6, 678-682 (June 1983), have also been suggested for use in detecting the presence of lupus anticoagulant. However, D. A. Triplett et al. demonstrated that the TTI procedure is not specific for lupus anticoagulants and thus does not provide a desirable test for detecting systemic lupus. Additionally, the PNP, while having been demonstrated to be sufficiently sensitive for qualitative determination of lupus anticoagulant, see V. Dayton et al., Laboratory Medicine, January 1990, pp. 30-32, does not provide a test for qualitative and quantitative study of platelet activity, and relies upon the addition of freeze-thawed platelets to neutralize the lupus anticoagulant.
In addition to detection of systemic lupus, there are also many other conditions which contribute to the need and desire of sensitive, reliable tests for platelet activity. For instance, it has long been known that aspirin (ASA) inhibits the activity of platelets in the coagulation system by suppressing their release of PF3. This, in turn, can lead to extended coagulation times for blood and plasma of patients taking aspirin. Nonetheless, as is well known, aspirin has been widely used as a pain killer and anti-inflammatory drug. Additionally, there has been a recent trend in medicine to prescribe a daily regimen of aspirin to reduce risk of heart attack. In fact, it has been estimated that over 20 million people in the U.S. presently take at least one aspirin a day for this reason. Further, recent suggestions have been made that sufferers of migraine headaches can benefit from a daily regimin of aspirin, and this could lead to over two million additional persons in the U.S. on daily aspirin therapy. This extensive and rapidly growing use of aspirin, which has heretofore somewhat recklessly proceeded without monitoring its effect on the patients' platelets, gives rise to an urgent need for sensitive tests which can be used to monitor aspirin therapy.
Another driving force for the development of good tests for platelet activity is the existence of platelet function abnormalities in patients. As an example, it has been discovered that full-term pregnancy pre-eclamptic women often have prolonged bleeding times. This has been attributed to low platelet counts, and also in some instances is thought to be due to abnormalities in platelets. See, J. Ramanathan et al., Anesthesiol., 1989, 71, 188-191.
Additionally, in the area of quality control, a recent article points up the need for a sensitive test which can be used to differentiate platelet concentrates which retain functional integrity after storage from those which do not, and explains that there is presently no available method for accomplishing this. T. Hervig et al., Clin. Chem., 1990, 36 No. 1, pp. 28-31.
Moreover, the presence of antiphospholipid antibodies has been associated with the occurrence of premature fetal death syndrome, see, for instance, D. A. Triplett, College of American Pathologists Today, July 1989, Vol. 3, No. 7 p. 61, thus giving rise to an additional group which would benefit from more sensitive and accurate tests for the presence of antiphospholipid antibodies. Further, to date there are no tests known to applicant for the quantitative determination of Platelet Factor 4 (PF4). However, as is known, PF4 neutralizes heparin, and thus an accurate determination of a patient's PF4 level should be an important and routine part of the application and monitoring of heparin therapy.
Another area to which this invention relates is hemostatic agents, which are commonly used to control bleeding from wounds or from vessels during surgery. As an example, collagen preparations have been used as topical hemostatic agents. R. G. Mason et al., Haemostasis, 3, 31-45 (1974). Mason et al. report that the collagen preparations apparently accelerate formation of fibrin primarily by alteration of platelets rather than by direct action on the soluble components of the intrinsic coagulation system. In this regard, product literature for AVITENE, a microfibrillar collagen hemostat (MCH) available from Alcon Laboratories, Inc. of Forth Worth, Tex., also states that contacting the MCH with a bleeding surface attracts platelets which adhere to the fibrils and undergo the release phenomenon to trigger aggregation of platelets into thrombi in the interstices of the fibrous mass. Physician's Desk Reference (1987) pp. 588-589. In addition to topical hemostats, it is also known to use hemostatic pastes to stem bleeding from arteries during major surgery such as heart surgery. Despite these known hemostatic agents, there still exists a continuing need and desire for improved hemostatic agents. The applicant's invention also contemplates an improved hemostatic agent to address this need.
As is evident from the foregoing, there exists a continuing need for new, as well as more sensitive, accurate and reliable coagulation assays which can be used to determine coagulative properties of blood or plasma. There also exist needs for improvements in reagents for clotting tests, and in materials and methods for treating bleeding. The applicant's inventions address these needs.
Although the causes of abnormal blood clotting are many, one cause which has been of particular importance is an abnormal platelet condition which renders the platelets unable to aggregate, a phenomenon essential to normal clotting. This abnormal platelet condition can be either a deficiency in the number of platelets in the patient's blood, or a defect in the platelets.
As an example, it has been discovered that full-term pregnancy pre-eclamptic women often have prolonged bleeding times. This has been attributed to low platelet counts, and also in some instances is thought to be due to abnormalities in platelets. See, J. Ramanathan et al., Anesthesiol., 1989, 71, 188-91. Additionally, in the area of quality control, a recent article points up the need for a sensitive test which can be used to differentiate platelet concentrates which retain functional integrity after storage from those which do not, and explains that there is presently no available method for accomplishing this. T. Hervig et al., Clin. Chem., 1990, 36, No. 1, pp. 28-31.
Prior known and used tests for screening fir abnormal platelet conditions are expensive and complicated. For example, the test currently used clinically is known as a platelet aggregation test. Generally, this test is performed by using expensive reagents such as ristocetin, collagen, adenosine diphosphate, or other reagents. Since these reagents work poorly, a sensitive optical instrument is used to follow the reaction. These tests, because of their inherent insensitivity, yield little clinically useful results. Needless to say, this test is not only costly, but also time consuming. Moreover, it cannot be conducted in the physician's office, necessitating sending samples to specialized laboratories for testing.
What is therefore needed is an initial screen test for determining the capacity of a patient's platelets to aggregate which is simple, inexpensive, and which can be conducted rapidly in a physician's office. Depending on the outcome of this initial screen, further, more quantitative testing for platelet aggregation may or may not be indicated. The present invention addresses this need.